So I think what we're seeing here is fairly standard. I think it's just the way FreeBSD allocates memory. Note that while I only have ~8MB Free, I have 476MB Inactive. Look at yours, it's something similar too.

That's why I mentioned Cacti - as this server is monitored 24/7 I have a good baseline and this trend is abnormal. Load on the server has not changed. At this rate in another 24hrs it will start swapping to disk.

Load has not changed and memory usage has remained steady over the 11 days that this system has been on. What you're seeing is nothing to worry about? It's just the way that FreeBSD handles memory. Technically, memory you have available is the sum of Inactive, Buffered, and Free memory. Also, you haven't touched Swap yet, which further confirms that everything is fine.

What I am telling you is:
a) my top output is not showing a figure for CACHE
b) buffers and free mem are constantly declining

Please stay on topic, I'm not looking for a discourse on graph colours

Free and Buffers memory constantly declining doesn't mean memory leak. Memory that is not accessed any more becomes inactive; and can become active again. For more info ask FreeBSD VM developers. FreeBSD is not Linux (at least in VM design).

But it's still possible that user programs (and not kernel) actually have memory leaks.

You can't look at just one or two of the values. You have to compare all of them, over the same time period. They will fluctuate. So long as the total always remains the same, and so long as swap is never touched, you do not have a problem. If the total of all the different mem types increases, and if you start hitting swap, then you have a memory leak you need to track down.